Not Applicable
1. Field of the Invention
This invention relates to opto-couplers used to electrically isolate signals.
2. Prior Art
Traditional opto-couplers are made using a discrete GaAs based LED and a silicon detector. In the simplest opto-couplers the detector is a single device such as a PN junction diode, a bipolar transistor, an SCR, or a Triac. Detector chips may also include circuits such as amplifiers and various types of output buffer/drivers. Moreover, an additional silicon chip can be added such as an input buffer/driver for the LED. The input signal may be, for example, a TTL type which can not directly drive the LED. Linear opto couplers can also been made which can transmit a voltage or a current level to an output from an isolated input.
The GaAs based LEDs used in opto couplers typically emit light in the deep red region of the visible spectrum where silicon PN junction diodes are efficient at converting the LED light into an electrical signal.
This invention relates to opto-couplers which electrically isolate signals. It is the objective to show how to make an all silicon opto coupler using a forward biased silicon PN junction diode as the LED. With lattice damage added by, for example, not annealing an implant used to make the diode, the optical efficiency can be improved to make practical all silicon opto-couplers. Thus, the traditional discrete GaAs based LED used in existing opto-couplers is replaced with a silicon forward biased PN junction diode which has a lower xe2x80x9conxe2x80x9d voltage (1.6V versus 0.65V for silicon). Furthermore, the forward biased silicon PN junction LED can be easily and cheaply integrated into a silicon integrated circuit using standard silicon processing techniques.
It is another object of this invention to show how a light detector capable of responding to the light produced by a forward biased silicon PN diode can integrated into silicon using standard silicon processing methods. Specifically, the light produced by a forward biased silicon PN junction diode produces light at a peak wavelength of about 1.15 xcexcm which is poorly absorbed by silicon. Silicon has a light absorption coefficient of only 0.025% per micron at 1.15 xcexcm. Thus, silicon PN junction diodes can not be used to detect the light emitted by a forward biased silicon PN junction diode. However, Schottky barrier diodes can detect 1.15 xcexcm with a quantum efficiency of better than 10% and can be integrated into silicon using standard silicon integrated circuit processing. Furthermore, the methods describe herein permit multiple, bi-directional optical channels to be realized. Also, an [the] assembly technique makes use of the essentially transparent transmission of 1.15 xcexcm light through the silicon substrate of the integrated circuit.